1. Field of the Invention
The present invention relates to a toner used for the toner recycle system in image forming device utilizing electrophotographic techniques, such as copying machines, printers, facsimile machines, etc. in which a toner remaining on the surface of the photosensitive member after the process of transferring to a recording sheet is reused as the developer, and to a toner recycling type developing method using such a toner.
2. Description of Related Art
Dry developers used for development in the image forming devices utilizing electrophotographic techniques are classified into a two-component developer consisting of a toner and a carrier such as ferrite powder, iron powder, glass beads, etc., a magnetic single-component developer comprising magnetic powder in the toner, and a nonmagnetic single-component developer. The toner used in these developers is composed of a binder resin and a colorant as main components, and additives such as a wax for improving low temperature fixability to recording sheets, a charge control agent for affording a polarity (positive charging or negative charging). The toner can be produced after blending these materials in a prescribed ratio by processes of melting, kneading, pulverizing and classifying to produce a powder. The toner is then subjected to surface treatment with external additives such as silica, titanium oxide, alumina and fine resin particles in order to control fluidity, chargeability, cleaning ability, preservability, etc., and is finally used as a developer.
By the way, in recent, image forming devices for which a mechanism of reusing the toner (recycle system) is added to the developing device is provided for the purpose of resource conservation and reduction in costs. In these image forming devices, it is generally adopted a toner recycle system which comprises scraping off the toner remaining on the surface of the photosensitive member by a cleaning blade or fur brush and transferring the recovered toner to a developer container to blend with the developer accommodated in the container.
The image forming devices using such a recycle system, however, have a problem that fogging and toner dusting are remarkably caused in the process of copying a large number of sheets. This problem is believed to be caused by increasing the amount of fine particles by destruction of the toner in the developing device. Accordingly, a toner, which is hard to become fine particles by destruction, has been required.
As a means for solving the above-mentioned problem in the recycle system, it has been proposed to use polyester resin that is not easily form fine particles as the binder resin. However, the toner using the polyester resin has a problem of having poor environmental stability.
The toner using a styrene-acrylic (methacrylic) acid ester copolymer has a problem of easily forming fine particles because of having poor strength for destruction, though it is excellent in environmental stability.